Reciprocal conjugate pair feed system for antenna array



July 22, 1969 f MARSTON ETAL 3,457,509

RECIP ROCAL CONJUGATE PAIR FEED SYSTEM FOR ANTENNA ARRAY Filed April 29, 1966 2 Sheets-Sheet 1 E WW P/W v I v V 7,

DIGITAL DPS DPS DPS DPS DPS DPS PHASE SHIFTER v (PRIOR ART FIG. 1-.

FIG. 3

' INVENTORS ARTHUR E. MARSTON MAX 1.. msuss, JR.

ATTORNEY United States Patent US. Cl. 325-21 Claims ABSTRACT OF THE DISCLOSURE An antenna array system for simultaneously transmitting and receiving energy wherein the direction of transmission and reception can be independently controlled. The array consists of pairs of elements equidistant from the array center. Two controllable nonreciprocal phase shifters are connected between each pair of elements, one phase shifter being used to modify transmitted energy and the other phase shifter being used to modify received energy.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This application is a continuation-in-part of application Ser. No. 510,710, filed Nov. 30, 1965, for Conjugate Pair Feed System for Antenna Array.

The present invention relates generally to improvements in microwave and antenna array systems and the like and more particularly to new and improved microwave antenna array systems wherein nonreciprocal phase shifters are used in such a way as to eliminate the need for switching the phase shifters between the transmit and receive states and wherein independent control of the transmit and receive beam directions is achieved.

In the field of microwave antenna array systems it has been the general practice to employ a variable phase shifter for each element of an antenna array in order to steer the radiation pattern of the antenna array. Although such devices have served the purpose, they have not proved entirely satisfactory under all conditions of service for the reasons that considerable difiiculty has been experienced in the synchronization of the variable phase shifters, which synchronization is necessary for the phase shifters to track with each other and to result in the desired radiation pattern from the antenna array. Considerable difficulties also have been experienced in the high cost of maintaining these complex systems and the related apparatus required to vary the phase shifters in synchronism.

The general purpose of this invention is to provide a microwave antenna array system which embraces all the advantages of similarly employed systems and possesses none of the aforedescribed disadvantages. To attain this the present invention contemplates the use of latching-type nonreciprocal phase shifters in microwave anten na. array systems. A latching-type nonreciprocal phase shifter is one which requires no continuously applied electrical power in order to achieve a desired phase shift, but rather requires only an electrical pulse. These latchingtype nonreciprocal phase shifters are used in such a way as to obviate the need for switching the phase shifters between the transmit and receive states of the antenna array, and to allow independent control of the transmit and receive beam directions.

An object of the present invention is the provision of a microwave antenna array system which incorporates the use of latching-type nonreciprocal phase shifters.

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Another object is to provide a system of the above description which isless complex and less costly to maintain than previous microwave antenna array systems.

A further object of the invention is the povision of a microwave antenna array system which obviates the need for switching the phase shifters between the transmit and receive states.

Another object of the invention is to provide for simplified phase shifter control.

Still another object is to provide a system of the above description which achieves independent control of the transmit and receive beam directions.

Other objects and features of the invention will become apparent to those skilled in the art as the disclosure is made in the following description of a preferred embodiment of the invention as illustrated in the accompanying sheets of drawings in which:

FIG. 1 shows a block diagram of a prior art antenna array system;

FIG. 2 illustrates a schematic View of one embodiment of the invention; and

FIG. 3 shows a block diagram of another embodiment of the invention.

Referring nOW to the drawings, there is shown in FIG. 1 a prior art antenna array system including a signal source 5 which supplies radio-frequency Waves to the antenna array 6 through digital phase shifters, indicated as DPS, wherein one digital phase shifter is required for each element of the antenna array 6. Such prior art systems are not capable of the independent control of the transmit and receive beam directions and as a result if it is desired to transmit a beam in one direction and to receive a second beam from another direction it is necessary to do this on a time sharing basis and to shift the digital phase shifters accordingly. In such prior art systems, therefore, it is not possible to transmit in one direction and to receive from another direction simultaneously.

Referring now to FIG. 2, there is shown a signal source 11 the output of which is electrically connected to a conventional transmit-receive circuit 12, which allows the simultaneous transmission and reception of signals. One output of the transmit-receive circuit 12 is electrically coupled to receiver 13, and a second output of the transmit-receive circuit 12 is electrically connected to a conventional phase-correcting feed network 14, which provides output signals that are in phase with each other.

One output 18 of the network 14 is fed into T-junction 15 which divides into branch lines 16 and 17, which may be cables or wave guides. The branch line 16 is connected to circulator 19 and the branch line 17 is connected to circulator 29. Located between circulators 19 and 29, and electrically connected thereto is nonreciprocal phase shifter 30. This phase shifter is nonreciprocal because a signal traversing it in one direction may undergo a different amount of phase shift than a signal traversing it in the opposite direction. The circulator 19 is in turn, electrically coupled to circulator 39 and the circulator 29 is electrically coupled to circulator 49. Located between the circulators 39 and 49 and electrically connected thereto is nonreciprocal phase shifter 20. As is shown in FIG. 2 by the various arrow symbols and will subsequently be more readily apparent, energy traveling from point 15 toward antenna elements E and E will not enter phase shifter 30 but will traverse phase shifter 20 While energy traveling in the other direction, i.e. from the antenna elements E and E toward point 15, will not enter phase shifter 20 but will traverse phase shifter 30. The nonreciprocal phase shifter 20, as illustrated comprises five phase-shift bits 21, 22, 23, 24 and 25 totalling 360", each including a circulator 21', 22', 23', 24' and 25', respectively, and a shorted transmission line 21", 22", 23", 24" and 25", respectively, each of which lines acts as a phase shifter and which is connect- Patented July 22, 1969 ed to one port of its respective circulator. As shown in FIG. 2 each phase shift unit is a two port nonreciprocal device which either shifts or does not shift the phase of a signal depending upon the direction of circulation of the circulator and the port to which the signal is applied. Referring specifically to unit 21 it can be seen that circulator 21' is set to have a counter-clockwise direction of circulation and therefore signals applied to port R undergo a phase shift of before they arrive at the entrance of circulator 22. This phase shift is due to the particular length of shorted transmission line 21". Signals traveling in the reverse direction, i.e. from circulator 22' to port R, pass through circulator 21 without traversing line 21" and therefore do not undergo the 20 phase shift.

The nonreciprocal phase shifter 30, as illustrated, also comprises five phase-shift bits 31, 32, 33, 34 and 35, totalling 360, each including a circulator 31, 32, 33, 34' and 35, respectively, and shorted transmission lines 31", 32", 33", 34" and 35", respectively, each of which lines acts as a phase shifter which is connected to one port of its respective circulator.

One port of circulator 21 is electrically connected to a port of circulator 39 and a second port of circulator 21' is electrically connected to a port of circulator 22'. A second port of circulator 22 is electrically connected to a port of circulator 23, and circulator 23' is similarly connected to circulator 24, which in turn is similarly connected to circulator 25; and one port of circulator 25 is electrically connected to a port of circulator 49.

In a similar manner, one port of circulator 31 is electrically connected ot .a port of circulator 19 and another port of circulator 31 is electrically connected to a port of circulator 32'. A second port of circulator 32 is electrically connected to a port of circulator 33, and circulator 33 is similarly connected to circulator 34, which in turn, is similarly connected to circulator 35'; and one port of circulator 35 is electrically connected to a port of circulator 29. The circulators 19, 29, 39 and 49 are shown as three-port circulators, but it should be understood that the two circulators 19 and 39 could be replaced by one four-port circulator as could be circulators 29 and 49.

The circulator 49 is then electrically connected to radiating element E, and circulator 39 is electrically connected to radiating element E, which elements are located in the linear antenna array 41 and an equal distance from the center 50 of the array.

If there is a center element 42 located at the center 50 of the array, the elements of each antenna element pair will be equal distances from the element 42, and the center element will be energized directly from the phase correcting network 14 by a transmission line (not shown).

Any number of phase-shift-bits of any magnitude may be used as long as they total 360, and phase shifters other than the shorted transmission line-circulator combinations could be used, such as nonreciprocal latchingtype ferrite phase shifters. While the shorted transmission line-circulator combination has been shown for convenience of illustration and description, it is contemplated that in practice the nonreciprocal latching-type ferrite phase shifters would be used. FIG. 3 symbolically illustrates the use of a multi-bit, nonreciprocal, latching-type ferrite phase shifter 44 connected in place of shorted transmission line-circulator combinations 20 and between points R and R. The reader will recognize, of course, that phase shifter 44 includes a plurality of switchable units of the nonreciprocal, digital-latching ferrite type arranged in a manner entirely analogous to the illustrated circulators 21-25 and 31-35. Various types of appropriate digital-latching phase shifters are discussed in an article entitled A Digital Latching Ferrite Strip Transmission Line Phase Shifter by L. R. Whicker and R. R. Jones appearing in IEEE Transactions on Microwave Theory and Techniques, vol. MTT-l3, No. 6, November 1965, pp. 781-784. An appropriate circulator for 4 use in FIG. 2 is disclosed in an article entitled Pulse- Operated Circulator Switch by L. Freiberg in IEEE Traansactions on Microwave Theory and Technique, May 1961, page 266.

In the operation of the microwave antenna array systern of FIG. 2 the signal entering at 11 is passed through the transmit-receive circuit 12 and into the phase-correcting feed network 14, which allows the electrical power to be in phase at the various inputs to the non-reciprocal phase shifters of the system, two of which are provided for each of the various antenna element pairs of the array (A-A, B-B, C-C, etc.), as exemplified by non-reciprocal phase shifters 20 and 30 which are provided for the antennielement pair E-E.

The signal from one output 18 of the phase-correcting feed network 14 is shown divided equally to left and right at T-junction 15 which passes the signals through branch lines 16 and 17 and into ports of circulators 19 and 29, respectively. The circulators 19 and 29 turn the two signals into the circulators 39 and 49, respectively. The circulators 39 and 49 then turn the signals into the nonreciprocal phase shifter 20 which comprises the series of phase-shift bits 21-25, which in turn include circulators 21-25 and phase-shifters 21-25".

By use of a computer (not shown) switching the action of the circulators 21-25 from right to left, or left to right, as may be necessary, can result in a phase shift equal to any multiple of 20 for the signal going from circulator 39 to circulator 49. As illustrated in FIG. 2 the signal passes unaltered through unit 23 but is modified by units 21, 22, 24 and 25 to be 280 lagging, which is, of course, the sum of the 20, 40, 160 and 60 lagging phase shifts encountered respectively in units 21, 22, 24 and 25. At the same time, since the sum of all the discrete phase shifts in the several phase shifters equals 360, the signal going from circulator 49 to circulator 39 will always be given a phase shift which is the conjugate of the phase shift imparted to the signal moving from circulator 39 to circulator 49. As illustrated in FIG. 2 this signal passes unaltered through units 25, 24, 22 and 21 but experiences in lagging phase shift in unit 23, which is, of course, equivalent to the 280 leading phase shift illustrated. The signals radiating from antenna elements E and E will therefore be conjugates and will contribute, according to well known array antenna theory, to the phase front transmitted.

It will be readily apparent that other clockwise and counterclockwise combinations of settings of units 21-25 are possible, and when accomplished together with appropriate settings of phase shifting units between other elements of the antenna array, will cause a differently directed phase front to be radiated. It is also readily apparent that this setting of the transmission phase shifter 20 can be accomplished entirely independently of the setting of the reception phase shifter 30.

When a signal is received back from the direction in which it was radiated, as represented in FIG. 2, the phase front will illuminate the antenna element E sometime before it will illuminate the antenna element E. With reference to the system shown in FIG. 2 the radiation illuminating the antenna elements E and E will be of conjugate phases, respectively, wherein the radiation illuminating antenna element E will be represented by a 280 lead and wherein the radiation illuminating antenna element E will be a 280 lag.

The energy from antenna elements E and B will pass into ports of circulators 39 and 49, respectively, which will turn the two signals into the circulators 19 and 29, respectively. The circulators 19 and 29 then turn the signals into the nonreciprocal phase shifter 30 which comprises the series of phase-shift bits 31-35 which in turn include circulators 31-35 and phase shifters 3l-35.

By use of a computer (not shown) switching the action of the circulators 31'35 from right to left, or left to right, as it may be necessary, can result in a phase shift equal to any multiple of 20 for the signal going from circulator 19 to circulator 29 (shown in FIG. 2 to be a phase advance of 280 or a phase lag of 80). At the same time, since the sum of all the discrete phase shifts in the several phase shifters equals 360, the signal going from circulator 29 to circulator 19 Will always be given a phase shift which is the conjugate of the phase shift imparted to the signal moving from circulator 19 to circulator 29. The phase shift of the signal moving from circulator 29 to circulator 19 is shown in FIG. 2 to be a phase lag of 280, and therefore as shown in FIG. 2, the signals emerging from the nonreciprocal phase shifter 30 will be in phase. These signals, in turn, are directed into ports of circulators 19 and 29 which turn the two signals into the branch lines 16 and 17, respectively, which in turn feed the signals into T-junction 15.

The energy from T-junction 15 is then fed through the line 18 and into the phase-correcting feed network 14. The function of the phase-correcting feed network 14 when the system is receiving the energy is to provide a signal having one phase from the inputs A-A, B B, C-C, D-D', etc.

The resultant signal from the phase-correcting feed network 14 is then fed into the transmit-receive circuit 12 which diverts the signal into receiver 13 while bypassing the signal source 11.

Although the system of FIG. 2 is represented as transmitting and receiving energy from the same direction, wherein identical control impulses from the computer (not shown) are used to activate the phase shifters 20 and 30, it should be clearly understood that the nonreciprocal phase shifters 20 and 30 can be controlled independently by the computer (not shown) so as to permit the transmission of energy in one direction while simultaneously receiving energy from another direction. In addition, it can be seen that contrary to the conjugate pair feed system which is the subject matter of copending application, Ser. No. 510,710, the instant invention obviates the need for switching the phase shifters between the transmit and receive states.

It can, therefor, be seen that the invention very effectively provides for the use of nonreciprocal phase shifters, and particularly for the use of latching-type nonreciprocal phase shifters in microwave antenna array systems in such a way as to provide for the independent control of the transmit and receive beam directions, and in such a way as to obviate the need for switching the phase shifters between the transmit and receive states. This reciprocal conjugate pair feed system for antenna arrays is well suited for satellite relay applications or for any other application where the ability to simultaneously transmit and receive is desired or where it is desired to have independent control of the transmit and receive beam directions.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of the United States is:

1. In a microwave antenna array, the combination comprising:

a pair of antenna elements predeterminedly spaced from the center of said array;

transmit-receive means functioning to produce and receive electrical signals;

first nonreciprocal, phase-shifting means functioning to produce a phase shift of a first predetermined magnitude in signals traveling in one direction therethrough and to produce a phase shift of conjugate magnitude to said first predetermined magnitude in signals traveling in the other direction therethrough;

second nonreciprocal, phase-shifting means functioning to produce a phase shift of a second predetermined magnitude in signals traveling in one direction therethrough and to produce a phase shift of conjugate magnitude to said second predetermined magnitude in signals traveling in the other direction therethrough; and

connecting circuit means connecting said pair of antenna elements, said transmit-receive means and said first and second nonreciprocal, phase-shifting means in such a manner that signals produced by said Transmit-Receive means travel through said first nonreciprocal, phase-shifting means in one direction to one of said pair of antenna elements and in the other direction to the other of said pair of antenna elements but do not travel through said second nonreciprocal, phase-shifting means and signals received by said Transmit-Receive means travel through said second nonreciprocal, phase-shifting means in one direction from one of said pair of antenna elements and in the other direction from the other of said pair on antenna elements but do not travel through said first nonreciprocal, phase-shifting means.

2. The combination of claim 1 wherein said first and second nonreciprocal, phase-shifting means comprise a plurality of nonreciprocal, latching-type phase shifters, each of said plurality of latching type phase shifters producing individual phase shifts, the sum of said individual phase shifts in said first nonreciprocal, phaseshifting means being equal to 360 and the sum of said individual phase shifts in said second nonreciprocal, phaseshifting means being equal to 360.

3. The combination of claim 2 wherein said nonreciprocal, latching-type phase shifters include a circulator and a shorted transmission line.

4. The combination of claim 2 wherein said first and second nonreciprocal, phase-shifting means include a plurality of nonreciprocal, latching-type ferrite phase shifters.

5. The combination of claim 2 wherein said connecting circuit means includes:

a T-junction having three ports, one of which is connected to said Transmit-Receive means;

first and second circulators each having three ports, the first ports of said first and second circulators being connected to said T-junction and the second ports of said first and second circulators being connected to said first nonreciprocal, phase-shifting means and third and fourth circulators each having three ports, the first ports of said third and fourth circulators being connected to the third ports of said first and second circulators, the second ports of said third and fourth circulators being connected to said second nonreciprocal, phase shifting means and the third ports of said third and fourth circulators being connected to said pair of antenna elements.

References Cited UNITED STATES PATENTS 3,276,018 9/1966 Butler 343854 RALPH D. BLAKESLEE, Primary Examiner A. J. MAYER, Assistant Examiner US. Cl. X.R. 343-854 

